The program project is aimed at understanding how diets high in fat lead to increased levels of defended body weight. Our overall strategy is to explore a model of dietary obesity at many levels and from multiple perspectives. The Animal &Physiology Core consolidates and centralizes the production of obese rats and their various control groups for each of the specific projects. Specifically, this core generates EVERY animal that is used in each of the specific projects and thereby assures that each experiment enjoys animals that have been treated in an identical manner, thus allowing comparisons across time, cohorts and projects. There are four primary goals of this core. 1) To generate requisite animals for the individual projects in any of the various dietary groups described in detail in the introductory section to the proposal. These groups include rats on a low-fat, semi-purified butter oil-based diet (LF), rats on a matched high-fat, semi-purified diet (HF), rats receiving the HF diet but with calories matched (pair-fed) to intake of the LF rats (PHF), rats receiving the LF diet and food-restricted by the same amount as the PHF: pair fed rats (PLF), and rats with pelleted chow (CHOW). The Core also generates control rats on HF and LF diets based on olive oil as opposed to butter oil. 2) To develop novel or modified rat surgical techniques as required by each of the individual projects. 3) To carry out experiments on behavioral aspects associated with the palatability and meal pattern analysis as well energy expenditure measurements to determine how the different fatty acids influence consumption and behaviors associated with body weight regulation. 4) To carry out carcass analysis for body lipid content on subjects from each of the individual projects. This includes non-invasive (i.e., NMR readings) and terminal assessments for the entire carcass or specific anatomical subareas (e.g., subcutaneous fat). Lastly, The Animal &Physiology Core will carry out certain pilot or other experiments necessary for creating data that are relevant and critical to the other projects. The Animal/Physiology Core personnel are already facile with all of the techniques required to date that are used to characterize the model; consequently the personnel are already well-trained and the protocols are all in place to efficiently accomplish the goals of this essential core.